(a) Technical Field
The present disclosure relates, generally, to a method for reducing the vibrations in a hybrid electric vehicle. More particularly, the present invention relates to a method for reducing backlash vibrations in a hybrid electric vehicle, in which the backlash vibration that is generated between a motor and a driving wheel can be easily reduced by slipping a clutch in an automatic transmission when the direction of a motor driving torque is suitably changed while the hybrid electric vehicle is running in electric vehicle (EV) mode.
(b) Background
Hybrid electric vehicles are vehicles that use an engine in combination with an electric motor as an auxiliary source of power to be able to promote a decrease in exhaust gas and an increase in fuel efficiency. In the power train system of a parallel hybrid electric vehicle, for example as shown in FIG. 3, an engine 10, an electric motor 20, and an automatic transmission 30 are directly connected with each other on an axis, and a clutch 40 is suitably arranged between the engine 10 and the electric motor 20. Further, in order to drive these components, an integrated starter generator 70 is directly connected with a crank pulley of the engine through a belt, and a rechargeable high-voltage battery 50 is suitably connected with the electric motor 20 through an inverter 60.
Preferably, in this hybrid electric vehicle, electric vehicle (EV) driving mode, i.e. EV only mode, suitably transmits only power of the electric motor 20 to a driving wheel 80 through the automatic transmission 30. For example, after being started, the hybrid electric vehicle is suitably driven by the electric motor.
Further, when the clutch 40 arranged between the engine 10 and the electric motor 20 is suitably activated to transmit power of the engine 10 to the driving axle, the hybrid electric vehicle (HEV) driving mode uses both the power of the engine 10 and the power of the electric motor 20, and more particularly uses the power of the engine 10 as main power and the power of the electric motor 20 as auxiliary power in the event of medium-speed traveling or high-speed traveling.
Further, driving modes of the hybrid electric vehicle include the regenerative braking mode in which the electric motor 20 is suitably generated to charge inertial energy of the vehicle to the battery during deceleration.
Preferably, since the engine power can be switched by the clutch, the electric motor 20 is suitably generated to recover the inertial energy so as to charge the battery 50 when no battery charging limitation is imposed (i.e., when the clutch is not coupled).
In this hybrid electric vehicle, the automatic transmission 30 is suitably arranged between the electric motor 20 and the driving wheel 80, and a final reduction gear (not shown) is suitably connected with the automatic transmission 30, etc. and includes gear elements having a backlash characteristic, but is short of a damping element such as a torsional damper. As a result, vibrations are caused by backlash when the direction of an effective transfer torque is changed.
This vibration phenomenon is mainly caused in the event of a creep start by backlash accumulation of the gear elements between the electric motor and the driving wheel. The vibration phenomenon creates a contrast with a desired image of consumers who may view the hybrid electric vehicle as a next-generation eco-friendly vehicle, and as a result the net drivability of the vehicle may be affected.
Thus, a preferred method of reducing the vibrations caused by the backlash includes, for example, a passive damping method of separately mounting a physical damping element such as a physical torsional damper, an active damping method of actuating damping force in the opposite direction of the vibrations on the basis of closed loop control, a torque profiling method of deforming the input torque of a backlash mechanism to inhibit generation of the vibration, and so on.
In the passive damping method, since a separate damper is additionally mounted on a power train system, there is a packing problem that results from the addition of the damper, and there is also an increased cost. In the case of the active damping method, design of a high-performance sensor and observer is essentially required, and performance is reduced in a specified situation where vibrations having causes other than the backlash, as in an uneven road, occur.
Further, in the case of the torque profiling method, since various types of torque deformation are taken into consideration, it is possible to apply control of suitably reducing the rate of torque variation in the neighborhood of a position where the backlash occurs. However, it is difficult to secure perfect vibration reduction performance in the process where torque response performance is traded off against vibration reduction performance.
Accordingly, there remains a need in the art for an additional vibration-reducing plan to apply both the active damping method and the torque profiling method, to make up for vibration reduction performance of the two methods, and to suitably cause no interference because similar vibration-reducing plans interfere with each other.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.